# Class: Extension

## ProtoBuf .Reflect. Extension

#### new Extension(buildernon-null, parentnon-null, name, fieldnon-null)

An extension (field).

##### Parameters:

Name | Type | Description
--- | --- | ---
`builder` | ProtoBuf.Builder | Builder reference
`parent` | ProtoBuf.Reflect.T | Parent object
`name` | string | Object name
`field` | ProtoBuf.Reflect.Message.Field | Extension field

Source:
  - protobuf.js, line 3939

### Members

#### (non-null) field :ProtoBuf.Reflect.Message.Field

Extended message field.

##### Type:

- ProtoBuf.Reflect.Message.Field

Source:
  - protobuf.js, line 3947